Abstract

A search for charged Higgs bosons decaying into a top quark and a bottom quark is presented. The data analysed correspond to 139 fb−1 of proton-proton collisions at sqrt{s} = 13 TeV, recorded with the ATLAS detector at the LHC. The production of a heavy charged Higgs boson in association with a top quark and a bottom quark, pp → tbH+ → tbtb, is explored in the H+ mass range from 200 to 2000 GeV using final states with jets and one electron or muon. Events are categorised according to the multiplicity of jets and b-tagged jets, and multivariate analysis techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass; they range from 3.6 pb at 200 GeV to 0.036 pb at 2000 GeV at 95% confidence level. The results are interpreted in the hMSSM and {M}_h^{125} scenarios.

Highlights

  • Background modellingWith the isolation criteria applied both at the trigger and analysis level, as well as the purity-enhancing identification criteria used for electrons and muons, the background due to non-prompt leptons is expected to be negligible

  • There are about 170 nuisance parameters considered in the fit, the number varying slightly across the range of mass hypotheses

  • Depending on the particular H+ mass hypothesis, the total systematic uncertainty is dominated by the uncertainties in the modelling of the ttbackground, in particular tt + ≥1b and tt + ≥1c, jet flavour-tagging uncertainties, and jet energy scale and resolution

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Summary

Data and simulation samples

The data used in this analysis were recorded with the ATLAS detector at the LHC between √. The production of tt + jets events was modelled using the Powheg-Box [50,51,52,53] v2 generator in the five-flavour scheme (5FS), which provides matrix elements (ME) at NLO in QCD, with the NNPDF3.0NLO PDF set [54]. The production of ttH events was modelled in the 5FS using the Powheg-Box [74] generator at NLO with the NNPDF3.0NLO PDF set. Other minor backgrounds (tHjb, tHW , tZq, tZW and four top quarks) were simulated and accounted for, even though they contribute less than 1% in any analysis region All samples and their basic generation parameters are summarised in table 1. In all samples the top-quark mass was set to 172.5 GeV, and the decays of b- and c-hadrons were performed by EvtGen v1.2.0 [79], except in samples simulated by the Sherpa event generator

Object reconstruction and event selection
Background modelling
Analysis strategy
Systematic uncertainties
Results
Conclusion
Full Text
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